Dampling alloy, process for producing the same, and damping part or vibration-proof product comprising or employing the same

ABSTRACT

A manganese-based damping alloy having stable damping properties; a process by which the damping alloy can be obtained without fail; and a damping part or vibration-proof product comprising or employing the damping alloy. A damping alloy made up of from 16.9 to 27.7 wt% copper, from 2.1 to 8.2 wt% nickel, from 1.0 to 2.9 wt% iron, 0.05 wt% or less carbon, 0.06 wt% or less oxygen, 0.06 wt% or less nitrogen, and manganese and unavoidable impurities as the remainder. Due to this constitution, nonmetallic inclusions such as carbides generate in a reduced amount and the manganese-based alloy can be pure. Consequently, the formation of a twin-crystal structure during heat treatment is accelerated and factors which inhibit the twin-crystal structure from moving upon stress imposition are diminished, whereby damping properties can be improved.

FIELD OF THE INVENTION

[0001] The present invention relates to a manganese-based damping alloyhaving stable damping properties, a process for producing the same, anda damping part or vibration-proof product which comprises or employs thealloy.

BACKGROUND OF THE INVENTION

[0002] Manganese-based damping alloys of the twin crystal type areknown, which are excellent in processability, formability, and otherproperties and effective in diminishing vibrations and noises (see,Japanese Patent 2,849,698).

[0003] The manganese-based damping alloys contain from 61 to 80 wt%manganese, which has a low melting point (1,244° C.) and a high vaporpressure, in contrast to iron-based alloys.

[0004] Because of this, when the melting method ordinarily used foriron-based alloys is used for melting the manganese-based dampingalloys, the following problems arise.

[0005] (1) In the case where the atmosphere used for melting has a highpartial oxygen pressure (PO₂), an oxide (MnO) is yielded in a largeamount through an oxidation reaction (Mn+O→MnO) because manganese has ahigh affinity for oxygen. Since this oxide inhibits the growth of atwin-crystal structure in the manganese-based damping alloys, theresultant damping alloys have reduced damping properties.

[0006] (2) In the case where the atmosphere used for melting has a lowpressure (i.e., a high vacuum), the amount of manganese which vaporizesduring the melting increases due to the high vapor pressure ofmanganese. This makes it difficult to stably obtain a manganese contentin a given range.

[0007] (3) In case where the manganese-based alloys are melted at atemperature of 1,500° C. or higher, manganese vaporizes in a largeramount due to the high vapor pressure of manganese. Consequently, thiscase also results in unstable manganese contents.

[0008] (4) The oxide (MnO) yielded during melting is apt to form alow-melting eutectic structure. There is hence a possibility that theoxide might damage the refractory constituting the melting vessel tothereby considerably shorten its life or arouse a melt leakage troubledue to a local damage by fusion.

SUMMARY OF THE INVENTION

[0009] An object of the present invention is to eliminate the problemsof related-art techniques described above and to provide amanganese-based damping alloy having stable damping properties. Anotherobject of the present invention is to provide a process by which thedamping alloy can be obtained without fail. Still another object of thepresent invention is to provide a damping part or vibration-proofproduct comprising or employing the damping alloy.

[0010] As a result of intensive investigations and researches made bythe present inventors, the present invention has been achieved, whichovercomes the problems described above, based on the idea that variousconditions for melting should be fixed and impurities which come intomanganese-based damping alloys should be diminished.

[0011] The present invention provides a damping alloy which comprisesfrom 16.9 to 27.7 wt% copper, from 2.1 to 8.2 wt% nickel, from 1.0 to2.9 wt% iron, 0.05 wt% or less carbon, 0.06 wt% or less oxygen, 0.06 wt%or less nitrogen, and manganese and unavoidable impurities as theremainder.

[0012] Due to the constitution described above, in which the contents ofcopper, nickel, and iron have been regulated within the given ranges andthe carbon, oxygen, and nitrogen contents have been limited, not onlymanganese vaporization can be prevented from resulting in an increase inthe relative concentration of carbon, oxygen, or nitrogen, but also itis possible to prevent an increase in oxygen content due to oxygencontamination, etc. As a result, the amount of nonmetallic inclusions(carbides, oxides, and nitrides) which are generated in the alloy isreduced and the alloy composition can be pure, whereby the formation ofa twin-crystal structure during heat treatment is accelerated andfactors which inhibit twin crystals from moving upon stress impositionare diminished. Thus, damping properties can be improved.

[0013] Consequently, the damping alloy can exhibit its dampingproperties even in a large-strain region and has stable mechanicalstrength. Therefore, a damping part which is nonmagnetic and excellentin formability/processability and in weldability or a vibration-proofproduct employing the damping part can be easily provided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] By way of example and to make the description more clear,reference is made to the accompanying drawing in which:

[0015]FIG. 1 is a diagrammatic view illustrating the melting step in theproduction process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Unless otherwise indicated, the content of the element is % byweight based on the total weight of the damping alloy (referred to as“wt%” hereinafter).

[0017] An explanation is given below on the range of the content of eachcomponent of the damping alloy.

[0018] Copper is contained in an amount of from 16.9 to 27.7 wt%. Thisis because copper contents lower than 16.9 wt% do not result in theformation of twin crystals, while copper contents exceeding 27.7 wt%result in a higher degree of copper segregation, making it impossible toattain desired damping properties. The more preferred range of coppercontent is from 19.7 to 25.0 wt%, and further preferably from 20.8 to23.8 wt%.

[0019] Nickel is contained in an amount of from 2.1 to 8.2 wt%, thereasons for which are as follows. Addition of nickel as the thirdelement in addition to manganese and copper gives desired dampingproperties. However, nickel contents lower than 2.1 wt% do notcontribute to the formation of twin crystals. On the other hand, evenwhen the nickel content is increased beyond 8.2 wt%, the effect offacilitating twin-crystal formation is not heightened any more.

[0020] Iron is contained in an amount of from 1.0 to 2.9 wt%, thereasons for which are as follows. Addition of iron as the fourth elementin addition to manganese, copper, and nickel enables desired dampingproperties to be obtained. However, iron contents lower than 1.0 wt% donot contribute to the formation of twin crystals. On the other hand,even when the iron content is increased beyond 2.9 wt%, the effect offacilitating twin-crystal formation is not heightened any more.

[0021] The contents of carbon and nitrogen have been regulated to 0.05wt% or lower and 0.06 wt% or lower, respectively. The reasons for thisare as follows. In case where the content of carbon or nitrogen ishigher than the upper limit, manganese vaporization results in anincrease in the relative concentration of carbon or nitrogen, making itimpossible to attain desired damping properties.

[0022] The content of oxygen has been regulated to 0.06 wt% or lower.This is because when the content of oxygen is higher than the upperlimit, the damping alloy has increased MnO and oxygen contents due tooxygen contamination.

[0023] The present invention further provides a process for producing adamping alloy which includes a melting step in which a raw damping-alloymaterial comprising from 16.9 to 27.7 wt% copper, from 2.1 to 8.2 wt%nickel, from 1.0 to 2.9 wt% iron, and manganese and unavoidableimpurities as the remainder is melted at a temperature in the range offrom the temperature higher by 50° C. than the melting point of thealloy (from 960 to 1,140° C.) to 1,480° C. in an inert atmosphere havinga partial oxygen pressure of 1,013.25 Pa (0.01 atm) or lower and a totalpressure of 66,661 Pa or higher.

[0024] In this process, the formation of an oxide (MnO) can be inhibitedbecause of the reduced partial oxygen pressure of the melting atmosphereand, hence, the growth of a twin-crystal structure can be accelerated.In addition, since the pressure of the inert gas constituting thisatmosphere is regulated to a value within that range, manganesevaporization can be prevented and the content of this component can bestably regulated so as to be within the range specified above.Furthermore, since the heating temperature for melting is in the rangeof from the temperature higher by 50° C. than the melting point of thedamping alloy to 1,480° C., manganese vaporization can be prevented andthe content of this component can be stably regulated so as to be withinthe range specified above. Consequently, the damping alloy describedabove, which has reduced carbon, oxygen, and nitrogen contents, can beproduced through melting without fail. The content of Mn is preferablyfrom 63.5 to 77.5 wt%, more preferably 66.5 to 74.5 wt%.

[0025] Examples of the inert gas include argon, nitrogen, and mixturesof these. The degree of vacuum of 66,661 Pa corresponds to 500 Torr. Thereason why the lower limit of the melting temperature is higher by 50°C. than the melting point of the alloy (from 960 to 1,140° C.) is thatthis lower limit enables the melting of alloys having the compositiondescribed above to be carried out at temperatures higher than themelting points thereof.

[0026] On the other hand, the upper limit of the melting temperature is1,480° C. so as to inhibit manganese vaporization and prevent theformation of a eutectic of MnO with Al₂O₃. The more preferred range ofthe melting temperature is from 1,200 to 1,300° C. The process describedabove can include various steps to be conducted after the melting step.For example, the melting step may be followed by hot or cold forging,rolling, machining, and then heat treatment.

[0027] In the process of the present invention for producing a dampingalloy, the melting step preferably comprises charging the rawdamping-alloy material into a vessel comprising MgO—Al₂O₃ as arefractory and melting the raw material therein. In this process, sincea vessel comprising a refractory (MgO—Al₂O₃), which is a spinel (AB₂O₄)type material less reactive with MnO, chemically stable, and excellentin thermal shock resistance and corrosion resistance, is used, thevessel is prevented from suffering a damage, wearing, or local damage byfusion and a stable melting operation can be conducted without fail.

[0028] The present invention furthermore provides a damping part orvibration-proof product which comprises or employs a damping alloycomprising from 16.9 to 27.7 wt% copper, from 2.1 to 8.2 wt% nickel,from 1.0 to 2.9 wt% iron, 0.05 wt% or less carbon, 0.06 wt% or lessoxygen, 0.06 wt% or less nitrogen, and manganese and unavoidableimpurities as the remainder, the alloy having been formed into anecessary shape. In this part or product, the damping alloy describedabove has been applied to a vibrating part. Accordingly, the part orproduct has a reduced frequency dependence and can exhibit dampingproperties even in a large-strain region. The alloy of the presentinvention preferably shows a logarithmic decrement of larger than 0.2(exclusive).

[0029] For forming the damping alloy into a necessary shape, use may bemade of, for example, a known metal working process in which the dampingalloy produced through melting is subjected to casting, hot forging, orhot rolling and further to cold forging, cold rolling, pressing,cutting, etc. A combination of two or more of such forming steps mayalso be used. It is desirable to conduct heat treatment after theseforming steps. For example, as the heat treatment, the alloy ismaintained at γ (austenite) range for several hours (2 to 3 hours) andthen cooled at the cooling rate of 150° C./hr or less.

[0030] Embodiments of the damping part of the present inventiondescribed above include machine elements, tools for machining, bases orcasings of metal working apparatus, spacers, liners, pipes, radiatingplates, valves, engine parts, electronic parts, parts of sports goods,and fasteners for ducts or pipings.

[0031] Thus, damping parts capable of exhibiting the damping propertiescan be provided without fail.

[0032] Examples of the machine elements include bolts, nuts, screws,washers, bearings, springs, rotating shafts, and chains. Examples of thetools for machining include cutters, turning tools, shanks, and hammers.Examples of the metal working apparatus include lathes, millingmachines, drilling machines, NC machines, and machining centers.Examples of the electronic parts include printed wiring boards,capacitors, transistors, IC chips, transformers, and motor parts.Examples of the engine parts include piston rings, piston rods, and fuelvalves. Examples of the parts of sports goods include golf club heads,putter heads, and the frames of tennis or badminton rackets.

[0033] Embodiments of the vibration-proof product of the presentinvention described above include conveying apparatus, audio/videoappliances (including appliances comprising at least either of an audioappliance and a video appliance), medical machines or apparatus,precision measuring instruments, sensors, transportation machines orapparatus, domestic electrical appliances, industrial machines orapparatus, air-conditioning machines or apparatus, computers, printers,copiers, building materials for openings, opening/closing devices,sports goods, and writing materials. Thus, vibration-proof productscapable of exhibiting the damping properties can be provided withoutfail.

[0034] Examples of the conveying apparatus include various conveyors,escalators, elevators, hoists, and cranes. Examples of the audio/videoappliances include amplifiers, tuners, various players for phonographrecords, DVDs, or MDs, audio decks, video decks, speakers, microphones,headphones, various TVs, video cameras, digital cameras, and mobiletelephones.

[0035] Examples of the medical machines or apparatus include variousexamination apparatus, various operation-supporting instruments, anddental remedial machines or apparatus. Examples of the transportationmachines or apparatus include vehicles such as motor vehicles andelectric railcars, ships, aircraft, and products to be disposed aroundthe engines or driving units of these machines or apparatus (e.g., powersteerings, column units, fuel injection control units, and cylinderblocks). Examples of the domestic electrical appliances include washingmachines, refrigerators, electronic ovens, ovens, vacuum cleaners, dishwashers, electric fans, and garbage-treating machines.

[0036] Examples of the industrial machines or apparatus include variouspumps, motors, compressors, forklifts and fingers thereof, and chainsaws. Examples of the air-conditioning machines or apparatus include airconditioners, outdoor heat exchangers, and heat medium ducts. Examplesof the computers include various drives for hard disks or the like.Examples of the building materials for openings include automatic doorsand revolving doors. Examples of the opening/closing devices includecurtain-drawing devices for indoor use or for vehicles. Examples of thesports goods include baseball bats, tennis or badminton rackets, hockeysticks, oars for boats, ski poles, and goal posts and crossbars forsoccer or hockey.

[0037] Preferred modes for carrying out the present invention will beexplained below together with the drawing.

[0038]FIG. 1 illustrates the melting step in a production process forobtaining the damping alloy of the present invention.

[0039] A raw material for the damping alloy is prepared beforehand. Thisraw material comprises from 16.9 to 27.7 wt% copper, from 2.1 to 8.2 wt%nickel, from 1.0 to 2.9 wt% iron, and manganese and unavoidableimpurities as the remainder.

[0040] On the other hand, a melting apparatus (induction heating vacuumfurnace) 1 such as that shown in FIG. 1 is prepared. As shown in thefigure, the melting apparatus 1 comprises: a metallic main body 2 whichis airtight and has a nearly elliptic vertical section; a lid 3 placedon the main body 2; and a vessel 6 placed in the main body 2. A gassupply/exhaust pipe 5 connected to a vacuum pump or the like (not shown)is connected to the top of the lid 3. The vessel 6 has a cylindricalcontainer part 7 which is circular when viewed from the top sidethereof, as shown in FIG. 1. At least a surface layer of the containerpart 7 of this vessel 6 is made of a refractory comprising a spinel(AB₂O₄) type refractory (MgO—Al₂O₃) . A high-frequency induction coil 8has been helically wound around the outer periphery of the vessel 6 at agiven distance. This coil 8 has been connected to a high-frequency powersource (not shown).

[0041] First, the raw material is charged into the container part 7 ofthe vessel 6. Thereafter, the lid 3 is placed on the top of the mainbody 2 to tightly close the inside 4 of the melting apparatus 1. Afterthe apparatus 1 is evacuated, argon gas or the like is introduced intothe inside 4 to regulate the inside 4 so as to constitute an inertatmosphere having a partial oxygen pressure of 1,013.25 Pa (0.01 atm) orlower and a total pressure of 66,661 Pa (corresponding to 500 Torr).Subsequently, a given high-frequency current is caused to flow throughthe high-frequency induction coil 8 to inductively heat the raw materialin the container part 7. Thus, the raw material is heated beyond themelting point thereof and is melted to give a melt M. The melt M is keptin this molten state at a temperature in the range of from thetemperature higher by 50° C. than the melting point of the alloy (from960 to 1,140° C.) to 1,480° C. for a given time period.

[0042] During this heating period, the inside 4 of the melting apparatus1, which contains the vessel 6, is maintained so as to be an inertatmosphere having a partial oxygen pressure of 1,013.25 Pa or lower anda total pressure of 66,661 Pa or higher. Because of this, the generationof a manganese oxide (MnO) is inhibited and manganese vaporization canbe inhibited. Furthermore, since the temperature used for the melting isregulated so as to be in the range of from the temperature higher by 50°C. than the melting point of the damping alloy (from 960 to 1,140° C.)to 1,480° C., the formation of an MnO/Al₂O₃ eutectic structure, whichmay occur at around 1,500° C., can be prevented. Moreover, since thatsurface layer of the container part 7 in the vessel 6 which is incontact with the melt is made of a spinel refractory (MgO—Al₂O₃), thecontainer part 7 is less apt to react with MnO. Consequently, thesurface of the container part 7 is prevented from being rapidly damagedor worn or arousing a melt leakage trouble due to a local damage byfusion, whereby stable melting can be conducted.

[0043] Through the melting step described above, a nonmagnetic dampingalloy of the present invention is obtained which comprises from 16.9 to27.7 wt% copper, from 2.1 to 8.2 wt% nickel, from 1.0 to 2.9 wt% iron,0.05 wt% or less carbon, 0.06 wt% or less oxygen, 0.06 wt% or lessnitrogen, and manganese and unavoidable impurities as the remainder.This damping alloy not only exhibits damping properties even in alarge-strain region because a twin-crystal structure is apt to generate,but also has improved mechanical strength and, hence, excellentformability/processability and excellent weldability. This damping alloymay be formed in an ordinary manner. Specifically, a melt of the alloyis cast with a given mold to obtain an ingot, which is subjected to hotforging or hot rolling and then to cold forging, cold rolling, pressing,extrusion forming, or the like. The resultant shape may be subjected tocutting, bending, drawing, compression, or the like according to need.Thus, the various damping parts mentioned above which each have anecessary shape and size and the various vibration-proof productsmentioned above can be obtained.

[0044] Examples of the present invention will be explained belowtogether with Comparative Examples for the purpose of comparison.

[0045] A raw manganese-based-alloy material was prepared which consistedof 22.4 wt% copper, 5.2 wt% nickel, 2.0 wt% iron, and manganese andunavoidable impurities as the remainder. Five-kilogram portions of thisraw material were separately melted using the melting apparatus 1described above and argon gas under the melting conditions shown inTable 1 to thereby obtain damping alloys of Examples 1 to 4.

[0046] Furthermore, the same raw material as that described above wasmelted in portions of the same weight for almost the same time periodusing the melting apparatus 1, etc. under the conditions shown in Table1 to thereby obtain damping alloys of Comparative Examples 1 to 5. Thecontents of carbon, oxygen, and nitrogen in the damping alloy of each ofthe Examples and Comparative Examples produced through melting are alsoshown in Table 1. TABLE 1 Melting conditions Partial Impurity con-oxygen Melting tents of Mn—Cu— Mn pres- Pres- temper- Ni—Fe alloy con-sure sure ature (wt %) tent (Pa) (Pa) (° C.) Refractory C O N (wt %) Ex.1 510 66700 1200 MgO—Al₂O₃ 0.02 0.01 0.01 69.4 Ex. 2 1010 106700 1300MgO—Al₂O₃ 0.03 0.03 0.03 70.5 Ex. 3 1010 66700 1300 MgO—Al₂O₃ 0.02 0.050.05 69.5 Ex. 4 1010 66700 1450 MgO—Al₂O₃ 0.03 0.06 0.06 69.0 Comp. Ex.1 10130 66700 1300 MgO—Al₂O₃ 0.05 0.45 0.01 69.2 Comp. Ex. 2 1010 133001300 MgO—Al₂O₃ 0.13 0.21 0.14 65.4 Comp. Ex. 3 1010 66700 1600 MgO—Al₂O₃0.15 0.18 0.12 66.3 Comp. Ex. 4 1010 66700 1300 MgO 0.01 0.31 0.01 67.9Comp. Ex. 5 1010 66700 1300 Al₂O₃ 0.01 0.26 0.01 68.1

[0047] The damping alloy ingots of the respective Examples andComparative Examples were separately subjected to forging, rolling,machining, and then heat treatment to obtain tensile test pieces havinga shape as provided for in JIS. These test pieces were separatelysubjected to a tensile test in accordance with JIS Z 2241.

[0048] With respect to damping properties (vibration damping capacity),sheet samples having a thickness of 1 mm, width of 10 mm, and length of160 mm were produced for the respective Examples and ComparativeExamples separately from the test pieces described above and wereexamined for logarithmic decrement (δ), which is a measure of dampingproperties, by the center vibration method at room temperature.

[0049] In Table 2 are shown the found values of tensile strength(σ_(B)/MPa) obtained in the tensile test for each of the Examples andComparative Examples and the found values of logarithmic decrement (δ)determined by the center vibration method.

[0050] The values of logarithmic decrement were obtained when theamplitude distortion was 5×10⁻⁴. TABLE 2 Tensile Damping property Evalu-strength Evalu- (logarithmic decrement) ation (MPa) ation Example 1 0.27◯ 540 ◯ Example 2 0.26 ◯ 525 ◯ Example 3 0.25 ◯ 510 ◯ Example 4 0.22 ◯505 ◯ Comparative 0.20 Δ 295 X Example 1 Comparative 0.15 X 310 XExample 2 Comparative 0.12 X 325 X Example 3 Comparative 0.18 Δ 300 XExample 4 Comparative 0.19 Δ 315 X Example 5

[0051] Table 2 shows that the damping alloys of Examples 1 to 4 hadexcellent damping properties and a tensile strength as high as 500 MPaor above.

[0052] In Comparative Example 1, on the other hand, MnO generated in alarge amount because of the high partial oxygen pressure during melting.In addition, the alloy had an increased oxygen content due to oxygencontamination. As a result, the alloy of Comparative Example 1 hadslightly reduced damping properties and a reduced tensile strength. InComparative Example 2, manganese vaporization occurred in an increasedamount because the melting was conducted at a low pressure (at a highvacuum), resulting in increased carbon, oxygen, and nitrogen contents.As a result, the alloy of Comparative Example 2 was reduced in bothdamping properties and tensile strength.

[0053] In Comparative Example 3, manganese vaporization occurred in anincreased amount because of the too high melting temperature, resultingin increased carbon, oxygen, and nitrogen contents. Because of this,Comparative Example 3 gave the same results as in Comparative Example 2.

[0054] Furthermore, in Comparative Examples 4 and 5, the refractoryconstituting the vessel 6 in the melting apparatus 1 consisted only ofmagnesia (MgO) or alumina (Al₂O₃) , respectively. Because of this, theserefractories were damaged by fusion. As a result, oxygen in eachrefractory and manganese formed an oxide to cause oxygen contamination,resulting in an increased oxygen content. Consequently, the alloys ofComparative Examples 4 and 5 had slightly reduced damping properties anda reduced tensile strength.

[0055] The effects of those damping alloys according to the presentinvention and of the process for producing these through a melting stepwere ascertained from the results given above, and the advantagesthereof were demonstrated.

[0056] The present invention should not be construed as being limited tothe modes and the Examples described above.

[0057] When the damping alloy of the present invention is subjected toheat treatment after the forming step described above, a damping part orvibration-proof product in which excellent damping properties have beenactualized can be obtained.

[0058] The damping part of the present invention, which has beenobtained by imparting a necessary shape to the damping alloy of thepresent invention, is nonmagnetic. Because of this, even when anelectronic control circuit or magnetic sensor is used around the dampingpart, the part neither adversely influences the circuit or sensor norbrings about an operation error.

[0059] In the production process of the present invention, the apparatusto be used for the melting is not limited to the melting apparatus(induction heating vacuum furnace) 1 described above. It is possible toconduct the melting step using a vacuum (reduced-pressure) arc heatingfurnace, a vacuum (reduced-pressure) floatation melting furnace in whichthe melt does not come into contact with the refractory, or a vacuum(reduced-pressure) semi-floatation melting furnace.

[0060] Furthermore, examples of the writing materials as an embodimentof the vibration-proof product include a mechanical pencil or ball-pointpen which employs the damping alloy as the case or as an innercomponent, and further include a fountain pen employing the dampingalloy also as the nib.

[0061] The present invention can be suitably modified as long as this isnot counter to the spirit of the present invention.

[0062] As described above, the damping alloy of the present inventionhas the following advantages. Since the contents of copper, nickel, andiron have been regulated so as to be within the given ranges and thecarbon, oxygen, and nitrogen contents have been limited, manganesevaporization can be prevented from resulting in an increase in therelative concentration of carbon, oxygen, or nitrogen or from causingoxygen contamination. Consequently, the amount of nonmetallic inclusions(carbides, oxides, and nitrides) which generate in the alloy is reducedand the alloy composition can be pure. As a result, the formation of atwin-crystal structure during heat treatment can be accelerated andfactors which inhibit twin crystals from moving upon stress impositioncan be diminished. Thus, damping properties can be improved. Therefore,various kinds of vibrations can be damped without fail.

[0063] On the other hand, the process of the present invention forproducing a damping alloy has the following advantages. The formation ofan oxide can be inhibited because of the reduced partial oxygen pressureof the melting atmosphere and, hence, the growth of a twin-crystalstructure can be accelerated. In addition, since the pressure of theinert gas constituting this atmosphere is regulated to a value withinthe range specified above, manganese vaporization can be prevented andthe content of this component can be stably regulated so as to be withinthe range specified above. Furthermore, since the heating temperaturefor melting is regulated so as to be in the range specified above,manganese vaporization can be prevented and the content of thiscomponent can be stably regulated so as to be within the range specifiedabove. Consequently, a damping alloy which has reduced carbon, oxygen,and nitrogen contents and has excellent damping properties can beproduced through melting without fail.

[0064] According to the preferred embodiment of the process of thepresent invention for producing a damping alloy, since a vesselcomprising a refractory (MgO—Al₂O₃), which is a spinel type materialless reactive with MnO, chemically stable, and excellent in thermalshock resistance and corrosion resistance, is used, the vessel isprevented from suffering a damage, wearing, or local damage by fusionand a stable melting operation can be conducted without fail.

[0065] Furthermore, the damping part and vibration-proof product of thepresent invention, in which the damping alloy has been applied to avibrating part, can exhibit damping properties even in a large-strainregion due to the movement of a twin-crystal structure.

[0066] While the invention has been described in detail and withreference to specific embodiments thereof, it will be apparent to oneskilled in the art that various changes and modifications can be madetherein without departing from the scope thereof.

[0067] This application is based on Japanese patent application No.2002-057084 filed Mar. 4, 2002, the entire contents thereof being herebyincorporated by reference.

What is claimed is:
 1. A damping alloy which comprises from 16.9 to 27.7wt% copper, from 2.1 to 8.2 wt% nickel, from 1.0 to 2.9 wt% iron, 0.05wt% or less carbon, 0.06 wt% or less oxygen, 0.06 wt% or less nitrogen,and manganese and unavoidable impurities as the remainder.
 2. A processfor producing a damping alloy which comprises a step by melting a rawdamping-alloy material comprising from 16.9 to 27.7 wt% copper, from 2.1to 8.2 wt% nickel, from 1.0 to 2.9 wt% iron, and manganese andunavoidable impurities as the remainder at a temperature in the range offrom the temperature higher by 50° C. than the melting point of thealloy to 1,480° C. in an inert atmosphere having a partial oxygenpressure of 1,013.25 Pa or lower and a total pressure of 66,661 Pa orhigher.
 3. The process for producing a damping alloy of claim 2, whereinin the melting step, the raw damping-alloy material is charged into avessel comprising MgO—Al₂O₃ as a refractory and is melted therein.
 4. Adamping part or vibration-proof product which comprises a damping alloycomprising from 16.9 to 27.7 wt% copper, from 2.1 to 8.2 wt% nickel,from 1.0 to 2.9 wt% iron, 0.05 wt% or less carbon, 0.06 wt% or lessoxygen, 0.06 wt% or less nitrogen, and manganese and unavoidableimpurities as the remainder, said alloy having been formed into anecessary shape.
 5. The damping part of claim 4, which is one memberselected from the group consisting of machine elements, tools formachining, bases or casings of metal working apparatus, spacers, liners,pipes, radiating plates, valves, engine parts, electronic parts, partsof sports goods, and fasteners for ducts or pipings.
 6. Thevibration-proof product of claim 4, which is one member selected fromthe group consisting of conveying apparatus, audio/video appliances,medical machines or apparatus, precision measuring instruments, sensors,transportation machines or apparatus, domestic electrical appliances,industrial machines or apparatus, air-conditioning machines orapparatus, computers, printers, copiers, building materials foropenings, opening/closing devices, sports goods, and writing materials.